1. Field of the Invention
The present invention relates to an ink jet printer having a print misalignment detection sensor for detecting misalignment of an image printed on a paper.
2. Description of the Related Art
A conventional ink jet printer has a printing head for printing an image on a paper, and a print misalignment detection sensor for detecting misalignment of the image printed on the paper in order to correct the image misalignment. The printing head is held by a cradle mounted on a carriage which is controlled to move along the paper. When the cradle is moved by the carriage, the printing head is moved along the paper together with the cradle, and ejects ink to print an image on the paper.
The print misalignment detection sensor is mounted on the cradle holding the printing head, and is moved along the paper together with the cradle and the printing head as the cradle is moved by the carriage. The print misalignment detection sensor irradiates light onto the paper, and receives reflection light from the paper so as to output a signal corresponding to an intensity of the received light. Based on the output signal of the print misalignment detection sensor, misalignment of the image printed by the printing head on the paper is detected so as to make various adjustments for correcting the image misalignment.
The print misalignment detection sensor comprises: a light-emitting element for emitting light to be irradiated onto a paper; a light-receiving element for receiving reflection light reflected from the paper; and a support member fixed to the cradle for supporting these light-emitting element and light-receiving element. The support member has a light transmitting groove having a substantially U-shaped cross section to form a light transmitting path of light emitted from the light-emitting element, and also has a light receiving groove having a substantially U-shaped cross section to form a light receiving path to the light-receiving element. The support member has an opening on a cradle-mounting side thereof to mount the support member on the cradle. The print misalignment detection sensor is mounted on the cradle with the opening of the support member being open on the cradle-mounting side.
However, in such conventional printer, the light emitted from the light-emitting element causes irregular reflection in the light transmitting path and the light receiving path, so that a waveform of the output signal of the print misalignment detection sensor has noise generated therein. The reason for the irregular reflection is that the cross section of the light transmitting path and the light receiving path is U-shaped, and that the opening of the print misalignment detection sensor is open on the cradle-mounting side. This causes a problem that it is not possible to correctly detect misalignment of an image printed on a paper, and to properly correct the image misalignment.
Besides, there are several known printers with carriages having optical sensors for various purposes. For example, a known printer has an optical sensor for sorting print media (refer to e.g. Japanese-translated Laid-open Publication of International Patent Application 2003-512984). Another known printer has an optical sensor for detecting an image printed on a paper to correct an upper end position of a page (refer to e.g. Japanese Laid-open Patent Publication 2001-253149). Yet another known printer has an optical sensor for detecting position of a printing paper (refer to e.g. Japanese Laid-open Patent Publication 2000-109243). However, none of the technologies of these printers can solve the above-described problem.